An apparatus for operating a discharge lamp and lighting fixture having such an apparatus for discharge lamp are conventionally known, the lighting device being adapted to light a discharge lamp by rectifying an electric output voltage of a commercial AC power supply and then inverting the rectified power by an inverter circuit. In the apparatus and lighting fixture, if a power supply voltage applied to the lighting device varies to an extent of 10%, then an electric current supplied to the discharge lamp varies to an extent of about 15%. Therefore, an output varies greatly against a variation of an input voltage.
Such a discharge lamp cannot be fully lit with a inverter circuit output.
Further, an apparatus for operating a discharge lamp, having a soft start function, has to employ a large capacity resistor, and thereby becomes complex in its circuit arrangement. It has, therefore, been difficult to manufacture a low-cost device of a soft start function type, in consideration of manufacturing costs.